Plating Solution Recovery Apparatus and Plating Solution Recovery Method

ABSTRACT

A plating solution recovery apparatus for electroplating, the apparatus comprises a circulation tank; a sludge removing device; a concentrating device; an iron compound crystallizing device; an iron compound separating device; an iron compound redissolving device; an iron ion removing device; pipelines sequentially connecting the circulation tank, the sludge removing device, the concentrating device, the iron compound crystallizing device, the iron compound separating device, the iron compound redissolving device, and then the iron ion removing device in a downstream direction from a base point coincident with the circulation tank; a pipeline connecting from the iron ion removing device to the circulation tank; a pipeline connecting from the iron compound separating device to the circulation tank; and a flow path changing device connecting to the circulation tank and provided in at least one portion selected from a group of portions, respectively, between the sludge removing device and the concentrating device, between the concentrating device and iron compound crystallizing device, and between the iron compound crystallizing device and the iron compound separating device. With the apparatus being used, the plating solution can be recovered in the manner that sludge and iron are removed from the plating solution used for electroplating of a steel strip. Further, with the apparatus being used, even when stopping the operation of a device(s) related to iron removal, a continuous electroplating operation can be maintained without reducing the operation rate of the sludge removing device.

TECHNICAL FIELD

The present invention relates to a recovery apparatus and method that enable the reuse of a plating solution used for electroplating of a steel strip.

BACKGROUND ART

In order to continuously apply electroplating (such as, electrolytic tin plating, electrolytic chrome plating, electrolytic zinc plating, or electrolytic copper plating) of a steel strip, an electrolytic liquid or solution is stored in a plating bath, and the steel strip is passed into the liquid. In this case, the steel strip is set to the cathode and a plating metal (tin, chrome, zinc, or copper, for example) disposed opposite the steel strip is set to the anode, and voltage is applied thereto. Although a tin plated steel strip is called “tinplate”, a tin plated steel strip herebelow will be referred to as “electroplated steel strip”.

In such an electroplating process, sludge is mixed into the electrolytic liquid (“plating solution”, hereinbelow) stored in the plating bath. In description hereinbelow, “sludge” refers to an aggregate formed in such a manner that the oxide of the plating metal floats or precipitates in the plating solution. For example, in the case of tin plating, Sn(OH)₄ or the like forms sludge. When sludge in the plating solution increases, quality-affecting problems are caused due to scratches, for example.

Under these circumstances, various types of researches and studies are under way for removing sludges contained in plating solutions from plating baths.

For example, Japanese Unexamined Patent Application Publication No. 62-74486 discloses a technique for isolating and removing sludges by using a centrifugal separator. However, since the viscosity of the sludge is high in most cases, not only is a high power centrifugal separator necessary from separating and removing sludge for enabling sludge separation, but also it takes a long time for sludge separation.

In addition, Japanese Unexamined Patent Application Publication No. 2004-59940 describes a technique for precipitating and removing sludge by using precipitation tanks. However, since it takes a long time for precipitation of the sludge, normally many precipitation tanks are necessary to reduce the process time.

Further, a plating solution contains not only sludge, but also plating metal ion, iron ion, and the like ions. Among these ions, plating metal ions (tin ion, chrome ion, zinc ion, and copper ion, and the like) for forming plating layers on the steel strip surface do not have to be removed. However, the iron ion is dissolved by reaction of the steel strip with components of the plating solution to the extent that the electrolytic characteristics of the plating solution are impaired. This results in deterioration in the quality of the plating layer formed to coat the steel strip surface. In any one of the two techniques described above, removal of the iron ion is not taken into consideration.

In order to regenerate and reuse the plating solution while applying continuous electroplating onto the steel strip, not only sludge in the plating solution but also the iron ion has to be removed from the plating bath. However, it is difficult to remove both the sludge and iron ion at the same time in a processing step, so that the processing step has to be separated into a processing step for removing the sludge and a processing step for removing the iron ion, thereby to continuously carry out the series of the processing steps. In order to achieve such an operation, dedicated removing devices for the processing steps have to be disposed in series and synchronously operated and have to be supplied with the plating solution.

In the case of plating solution recovery by the sludge removing device and iron ion removing device being series disposed, even when failure occurs in one of the devices, the plating solution regenerating process, the whole of the plating solution recovery process has to be terminated, thereby reducing the productivity of the electroplated steel strip.

Accordingly, an object of the present invention is to provide a plating solution recovery apparatus and method that remove sludge and iron from a plating solution used for electroplating of a steel strip, thereby to enable the reuse of the plating solution and the improvement of productivity for electroplated steel strips.

DISCLOSURE OF INVENTION

The present invention provides a plating solution recovery apparatus for electroplating comprises a circulation tank; a sludge removing device; a concentrating device; an iron compound crystallizing device; an iron compound separating device; an iron compound redissolving device; an iron ion removing device; pipelines sequentially connecting the circulation tank, the sludge removing device, the concentrating device, the iron compound crystallizing device, the iron compound separating device, the iron compound redissolving device, and then the iron ion removing device in a downstream direction from a base point coincident with the circulation tank; a pipeline connecting from the iron ion removing device to the circulation tank; a pipeline connecting from the iron compound separating device to the circulation tank; and a flow path changing device connecting to the circulation tank and provided in at least one portion selected from a group of portions, respectively, between the sludge removing device and the concentrating device, between the concentrating device and iron compound crystallizing device, and between the iron compound crystallizing device and the iron compound separating device.

It is preferable that the plating solution recovery apparatus be an apparatus having the flow path changing device provided in the portion between the sludge removing device and the concentrating device. Alternatively, it is preferable that the plating solution recovery apparatus be an apparatus having the flow path changing device provided in the portion between the concentrating device and the iron compound crystallizing device. Still alternatively, it is preferable that the plating solution recovery apparatus be an apparatus having the flow path changing device provided in the portion between the iron compound crystallizing device and the iron compound separating device.

It is preferable that any one of the above-described plating solution recovery apparatuses further include a flow path changing device connecting to the circulation tank and provided in a portion between the iron compound redissolving device and the iron ion removing device.

The present invention further provides a plating solution recovery apparatus for enabling reuse of a plating solution used to apply electroplating onto a steel strip, the apparatus comprises a circulation tank for storing the plating solution; a sludge removing device for removing sludge in the plating solution supplied from the circulation tank; a plating solution concentrating device for concentrating the plating solution supplied from the sludge removing device; an iron precipitating device for precipitating an iron compound by cooling the plating solution supplied from the plating solution concentrating device; an iron separating device for separating the iron compound from the plating solution supplied from the iron precipitating device and for redissolving the iron compound in water; an iron removing device for removing an iron ion of a redissolved solution supplied from the iron separating device by means of an ion-exchange resin; and a flow path changing device for supplying the plating solution from the plating solution concentrating device to the circulation tank.

The present invention further provides an operating method for any one of the plating solution recovery apparatuses as described above. In the respective apparatus, when stopping at least one device from a group consisting of the concentrating device, the iron compound crystallizing device, the iron compound separating device, the iron compound redissolving device, and the iron ion removing device, the flow path for the plating solution is changed to the circulation tank on a side further upstream of a most-upstream side stopped device and in the at least one portion selected from the group of portions, respectively, between the sludge removing device and the concentrating device, between the concentrating device and iron compound crystallizing device, and between the iron compound crystallizing device and the iron compound separating device.

Preferably, in the operating method for the plating solution recovery apparatus, when stopping at least one device from a group consisting of the iron compound crystallizing device, the iron compound separating device, the iron compound redissolving device, and the iron ion removing device, the flow path for the plating solution is changed to the circulation tank on a side further upstream of a most-upstream side stopped device and in the at least one portion selected from the group of portions, respectively, between the sludge removing device and the concentrating device, between the concentrating device and iron compound crystallizing device, and between the iron compound crystallizing device and the iron compound separating device. Alternatively, it is preferable that the operating method for the plating solution recovery apparatus be a method in which, when stopping at least one device from a group consisting of the iron compound separating device, the iron compound redissolving device, and the iron ion removing device, the flow path for the plating solution is changed to the circulation tank on a side further upstream of a most-upstream side stopped device and in the at least one portion selected from the group of portions, respectively, between the sludge removing device and the concentrating device, between the concentrating device and iron compound crystallizing device, and between the iron compound crystallizing device and the iron compound separating device.

Preferably, in any one of the above-described operating methods for any one of the plating solution recovery apparatuses as described above, when stopping the iron ion removing device, the flow path for the redissolved solution is further chanted to the circulation tank in a portion between the iron compound redissolving device and the iron ion removing device.

Further, in any one of the above-described operating methods for any one of the plating solution recovery apparatuses as described above, it is preferable that the electroplating solution contain tin methanesulfonate.

The present invention further provides a plating solution recovery method for enabling reuse of a plating solution used for electroplating of a steel strip. In the method, after the plating solution stored in a circulation tank is supplied to a sludge removing device and sludge in the plating solution is removed; the plating solution is supplied to a plating solution concentrating device, and the plating solution is concentrated therein; the plating solution is supplied to an iron precipitating device, and iron in the plating solution is precipitated therein as an iron compound; the plating solution is supplied to an iron separating device, the iron compound is separated, and the separated iron compound is redissolved in water to be a redissolved solution; the redissolved solution is supplied to an iron removing device, and an iron ion is removed therein by means of an ion-exchange resin; and the plating solution from which the iron compound has been removed in the iron separating device and the redissolved solution from which the iron ion has been removed in the iron removing device are supplied to the circulation tank. When stopping operation of the iron precipitating device, the iron separating device, or iron removing device, the plating solution is supplied from the plating solution concentrating device to the circulation tank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing respective examples of devices (respectively, “sludge and iron ion removing devices”, herebelow) for removing sludge and iron ion by using the present invention.

FIG. 2 is a flow diagram showing other examples of sludge and iron ion removing devices for removing sludge and iron ion by using the present invention.

FIG. 3 is a flow diagram showing other examples of sludge and iron ion removing devices for removing sludge and iron ion by using the present invention.

FIG. 4 is a flow diagram showing devices operated for comparison.

BEST MODE FOR CARRYING OUT THE INVENTION

A plating solution for use in applying electroplating onto steel strips contains a plating metal ion, and hence has electrical conductivity. During the electrolyte plating operation, foreign matters, such as sludge and iron ion, are inevitably entrained into the plating solution. Such matters adversely effects quality of the steel strip surface and the electrolytic characteristics of the plating solution to the extent of interfering the electrolyte plating operation, such that the matters such as sludge and iron ion has to be removed from the plating solution.

The present invention is intended to be adapted to electroplating processes, such as tin, chrome, zinc, and copper plating processes. Especially, it is preferable that the present invention be adapted to the tin plating process that is relatively prone to cause the sludge and iron ion problem. More specifically, it is preferable that the present invention be adapted to tin plating processes using plating solutions, such as a methanesulfonic acid bath, halogen bath, and phenol sulfonic acid bath. Especially, the methanesulfonic acid bath is low in pH and hence is prone to dissolution of iron, such that it is more preferable that the present invention be adapted to methanesulfonic acid baths. As such, the following describes a case where the present invention is adapted to a methanesulfonic acid tin plating solution.

According to the present invention described and exemplified hereinabove, the plating solution stored in the plating layer is temporarily stored in a circulation tank, and the plating solution is supplied therefrom to devices for removing matters such as sludge and iron ion. Further, the plating solution recovered by removing the matters such as sludge and iron ion is returned to the circulation tank, the plating solution is circulated to the plating bath.

FIG. 1 is a flow diagram showing a procedure for removing sludge and iron ion by adapting the present invention. In FIG. 1, the example is shown in which a pump 9 is disposed on a discharge side of a circulation tank 1. However, the position of the pump 9 and the number of pumps 9 can be appropriately set corresponding to, for example, the flowrate of a plating solution 10 or specification of respective devices described below. Further, a plating bath is not shown.

The plating solution 10 is supplied from the circulation tank 1 to a sludge removing device 2. The sludge removing device 2 removes sludge contained in the plating solution 10. A conventionally known device, such as a filter, filter press, or centrifugal separator, is used for the sludge removing device 2. However, taking characteristics, such as viscosity and granularity, of sludge, it is preferable that a filter press be used.

Pipelines fluidly connecting to valves 13 a and 13 b working as a flow path changing devices 13 and to the circulation tank is disposed to the discharge side (downstream side) of the sludge removing device 2. When a series of devices, described below, are operated, the valve 13 b is closed, and the valve 13 a is opened. Thereby, the plating solution 10 is supplied to a solution concentrating device 3 from the sludge removing device 2. The solution concentrating device 3 concentrates the plating solution 10. As such, for the solution concentrating device 3, it is preferable that a device capable of vaporizing water by either heating or vacuum distillation be used. The concentration eases precipitation of an iron compound 11 in an iron compound crystallizing device 4 (alternatively, “iron precipitating device”, hereinbelow). The rate of concentration of the plating solution 10 in the solution concentrating device 3 can be appropriately set corresponding to, for example, the flowrate of the plating solution 10 or specifications of the respective devices described below. However, over-concentration results in an increase in the consumption of thermal energy, thereby leading to cost increases. In the case of a tin methanesulfonate plating solution, the plating solution is concentrated to, as a standard, about four times the methanesulfonic acid concentration of the plating solution 10 supplied from the sludge removing device 2.

According to the present invention described and exemplified hereinabove, the plating solution 10 is concentrated after removal of sludge contained in the plating solution 10. A reason therefor is that, when the plating solution 10 containing sludge is supplied to the solution concentrating device 3, it becomes difficult to remove thereafter.

FIG. 1 shows the example configuration in which the valves 13 a and 13 b are disposed as components of the flow path changing device 13. However, the flow path changing device 13 for use in the present invention is not limited to the configuration formed from such valves, but may be configured using devices conventionally used change the fluid flow path (such as a valve-open/close type device).

The plating solution 10 concentrated in the solution concentrating device 3 is supplied to an iron compound crystallizing device 4 (alternatively an “iron precipitating device 4”, hereinbelow). The iron compound crystallizing device 4 cools the plating solution 10 to thereby precipitate the iron compound 11 (iron methanesulfonate in the case of a tin methanesulfonate plating solution). The iron methanesulfonate is formed in the manner that the steel strip reacts with the methanesulfonic acid, which is a component of the plating solution. In the iron compound crystallizing device 4, while the state where the plating metal ion (that is, the tin ion) is dissolved in the plating solution 10 is being maintained, only the iron compound 11 is precipitated. As such, a cooling condition for cooling the plating solution 10 in the iron compound crystallizing device 4 is set to a temperature between a temperature for precipitation of the iron compound and a temperature for precipitation of the plating metal compound (that is, tin compound). For example, for the tin methanesulfonate plating solution, the cooling condition is set to a temperature (about −4° C.) between the iron methanesulfonate precipitation temperature and the tin methanesulfonate precipitation temperature.

Subsequently, the plating solution 10 and the iron compound 11 are supplied from the iron compound crystallizing device 4 to an iron separating device 5. The iron separating device 5 includes an iron compound separating device 6 and an iron compound redissolving device 7. The iron separating device 5 separates the iron compound 11 (iron methanesulfonate in the case of the tin methanesulfonate plating solution) from the plating solution 10 and redissolves the compound into water. For the iron compound separating device 6, a conventionally known device, such as a centrifugal separator or a filter, is used. However, in the present step, sludge has been already removed, so that the viscosity of a mixture of the plating solution 10 and the iron compound 11 is low, and the specific gravity of the iron compound 11 (that is, the iron methanesulfonate) is relatively large. Taking these facts into consideration, it is preferable that the centrifugal separator be used.

The plating solution 10, from which the iron compound 11 has been separated in the iron compound separating device 6, is then supplied to the circulation tank 1.

The iron compound 11 is supplied to the iron compound redissolving device 7. The iron compound redissolving device 7 redissolves the iron compound 11 (that is, the iron methanesulfonate) into water, and uses a water bath or the like. The water refers to water, such as distillate water, ion-exchange water, tap water, or industrial water, not containing methanesulfonic acids. An aqueous solution containing the dissolved the iron compound 11 (that is, the iron methanesulfonate) will be referred to as a “redissolved solution 12” herebelow.

The redissolved solution 12 is supplied from the iron compound redissolving device 7 to an iron ion removing device 8 (alternatively “iron removing device”, hereinbelow). The iron ion removing device 8 operates so that the iron ion in the redissolved solution 12 is substituted with protons, whereby the iron ion is removed by being adsorbed from the redissolved solution 12 to an ion-exchange resin. A plating solution component (that is, the methanesulfonic acid) is recovered for the redissolved solution 12 from which the iron ion has been removed, and the redissolved solution 12 is then supplied to the circulation tank 1 redissolved solution 12.

In this manner, sludge and iron ion are removed from the used plating solution 10 stored in the circulation tank 1, and the recovered plating solution 10 is returned to the circulation tank 1, is then returned to the plating bath, and is circulated and used.

When stopping the operation of at least one facility selected from a group consisting of the solution concentrating device 3, iron compound crystallizing device 4, iron compound separating device 6, iron compound redissolving device 7, and iron ion removing device 8 for the reason of, for example, failure or regular inspection, the valve 13 b of the flow path changing device 13 is opened, and the valve 13 a thereof is closed. As a consequence, the plating solution 10 is supplied to the circulation tank 1 from the sludge removing device 2. More specifically, even when the operation of a series or part of the devices from the solution concentrating device 3 to the iron ion removing device 8 related to iron removal is stopped, the plating solution 10 from which sludge has been removed in the sludge removing device 2 is supplied to the circulation tank 1. Thereby, a continuous electroplating operation can be maintained.

FIG. 2 is a flow diagram showing another example of an apparatus of the present invention. More specifically, the flow path changing device 13 of FIG. 1 is provided on the discharge side (downstream side) of the solution concentrating device 3. Similar to the operation of FIG. 1, when operating the series of devices, the valve 13 b is closed, and the valve 13 a is opened.

However, when stopping the operation of at least one facility selected from a group consisting of the iron compound crystallizing device 4, iron compound separating device 6, iron compound redissolving device 7, and iron ion removing device 8 for the reason of, for example, failure or regular inspection, the valve 13 b of the flow path changing device 13 is opened, and the valve 13 a thereof is closed. As a consequence, the plating solution 10 is supplied to the sludge removing device 2 from the solution concentrating device 3. More specifically, even when the operation of a series or part of the devices from the iron compound crystallizing device 4 to the iron ion removing device 8 related to iron removal is stopped, sludge is removed from the plating solution 10 in the sludge removing device 2, and the plating solution 10 concentrated in the solution concentrating device 3 is supplied to the circulation tank 1. Thereby, the continuous electroplating operation can be maintained.

FIG. 3 is a flow diagram showing another example of an apparatus of the present invention. More specifically, the flow path changing device 13 of FIG. 1 is provided on the discharge side (downstream side) of the iron compound crystallizing device 4. Similar to the operation of FIG. 1, when operating the series of devices, the valve 13 b is closed, and the valve 13 a is opened.

However, when stopping the operation of at least one facility selected from a group consisting of the iron compound separating device 6, iron compound redissolving device 7, and iron ion removing device 8 for the reason of, for example, failure or regular inspection, the valve 13 b of the flow path changing device 13 is opened, and the valve 13 a thereof is closed. As a consequence, the plating solution 10 is supplied to the sludge removing device 2 from the solution concentrating device 3. More specifically, even when the operation of a series or part of the devices from the iron compound separating device 6 to the iron ion removing device 8 related to iron removal is stopped, sludge is removed from the plating solution 10 in the sludge removing device 2 and is concentrated in the solution concentrating device 3, and then the plating solution 10 is supplied to the circulation tank 1. Thereby, the continuous electroplating operation can be maintained. In this case, while a precipitation of the iron compound is entrained into the plating solution 10, since it is dissolved in the circulation tank 1, the electroplating operation is not interfered.

Thus, the present invention is adapted to any one of the electroplating-dedicated plating solution recovery apparatus, operating method therefor, and electroplating solution recovery method. The recovery apparatus includes the flow path changing device 13, which fluidly connecting to the iron compound crystallizing device 4, in at least one of the portions, namely, the portion between the sludge removing device 2 and the solution concentrating device 3, the portion between the solution concentrating device 3 and the iron compound crystallizing device 4, and the portion between the iron compound crystallizing device 4 and the iron compound separating device 6.

As a matter of course, the technical scope of the present invention is inclusive of a plating solution recovery apparatus including three flow path changing devices 13 respectively pre-disposed in all the three portions and a plating solution recovery apparatus including two flow path changing devices 13 respectively pre-disposed in arbitrarily selected two of the three portions. As such, by use of any one of these apparatuses, valves or the like components of the flow path changing devices 13 are appropriately switched, thereby enabling the recovery of the electroplating solution.

Further, it is preferable that even any one of the above-described plating solution recovery apparatuses of the present invention further includes a redissolved solution flow path changing device 14 fluidly connecting to the circulation tank between the iron compound redissolving device 7 and the iron ion removing device 8.

More specifically, it is preferable that valves 14 a and 14 b working as the redissolved solution flow path changing device 14 and a pipeline fluidly connecting to the circulation tank be provided on the discharge side (downstream side) of the iron compound redissolving device 7.

An example of the configuration such as described above is shown in FIG. 3. When the iron ion removing device 8 is operated, the valve 14 b is closed, and the valve 14 a is opened. As such, in a normal operation, the redissolved solution 12 is supplied from the iron compound redissolving device 7 to the iron ion removing device 8.

When stopping the operation of the iron ion removing device 8 for the reason of, for example, facility failure or regular inspection, the valve 14 b of the flow path changing device 14 is opened, and the valve 14 a thereof is closed. As a consequence, the redissolved solution 12 is supplied to the circulation tank 1 from the iron compound redissolving device 7. More specifically, even when the operation of the iron ion removing device 8 is stopped, sludges are removed from the plating solution 10 in the sludge removing device 2, iron compounds are precipitated, and then the redissolved solution 12 containing the iron compound dissolve in water is supplied to the circulation tank 1. Thereby, the continuous electroplating operation can be maintained.

While the example is shown above in which the valves 14 a and 14 b are used as components of the redissolved solution flow path changing device 14, the redissolved solution flow path changing device 14 for use in the present invention is not limited to the configuration formed from such valves, but may be configured using devices conventionally used change the fluid flow path (such as a valve-open/close type device).

Further, even in any one of the exemplified plating solution recovery apparatuses of the present invention, either one or both of the redissolved solution flow path changing device 14 and flow path changing device 13 may be used.

While the description has been made referring to the cases where the tin methanesulfonate plating solution is used, the cases are merely examples of the present invention, various changes can be made corresponding to, for example, the type of the plating metal and the composition of the plating solution.

Thus, according to the present invention described and exemplified above, the plating solution recovery can be achieved in the manner that sludge and iron are removed from the plating solution used in electroplating. Further, according to any one of the plating solution recovery apparatuses described and exemplified, even when the operation of the device related to the iron removal, the continuous electroplating operation can be maintained without reducing the operation rate of the sludge removing device. Consequently, the productivity for electroplated steel strips can be improved.

EXAMPLE 1

A plating solution used in a plating bath disposed in a tinplate steel strip manufacturing line was supplied to a circulation tank. The plating solution used is a tin methanesulfonate plating solution, and matters such as sludge, iron ion, and tin ion are inevitably mixed into the plating solution. The plating solution was recovered by using the apparatus shown in FIG. 1.

As shown in FIG. 1, the plating solution 10 was supplied from the circulation tank 1 to the sludge removing device 2, and sludge was removed from the plating solution 10. For the sludge removing device 2, a filter press was used. In normal operation, the valve 13 b of the flow path changing device 13 disposed on the discharge side of the sludge removing device 2 was closed, and the valve 13 a of the flow path changing device 13 was opened. Thereby, the plating solution 10 was supplied to the solution concentrating device 3 from the sludge removing device 2. In the solution concentrating device 3, the plating solution 10 was vacuum distillated to vaporizing water, and was then concentrated to a four-times concentration with respect to the concentration of the methanesulfonic acid of the plating solution 10 supplied from the sludge removing device 2. The plating solution 10 concentrated in the solution concentrating device 3 was supplied to the iron compound crystallizing device 4, and was cooled therein to −4° C., whereby the iron methanesulfonate was precipitated. Then, the plating solution 10 and the precipitation were supplied to the iron compound separating device 6 of the iron separating device 5. Therein, the iron methanesulfonate precipitated in the iron compound separating device 6 was separated from the plating solution 10. A centrifugal separator or the like was used as the iron compound separating device 6. The plating solution 10, from which the iron methanesulfonate 11 has been separated in the iron compound separating device 6, was supplied to the circulation tank 1. The iron methanesulfonate 11 was supplied to the iron compound redissolving device 7, and was dissolved therein in industrial water. A redissolved solution 12 obtained thereby was supplied to the iron ion removing device 8, and was adsorbed therein to an ion-exchange resin. The redissolved solution 12, from which the iron ion was removed, was then supplied to the circulation tank 1.

When stopping the operation of at least one of the solution concentrating device 3, iron compound crystallizing device 4, iron compound separating device 6, iron compound redissolving device 7, and iron ion removing device 8, the valve 13 b of the flow path changing device 13 was opened, and the valve 13 a thereof was closed. Thereby, the plating solution 10 was supplied to the circulation tank 1 from the sludge removing device 2. The above is referred to as an inventive example.

Further, as a comparative example, the plating solution used was recovered by using an apparatus shown in FIG. 4. The apparatus operates in substantially the same manner as in the inventive example in the normal operation. However, when stopping the operation of at least one of the solution concentrating device 3, iron compound crystallizing device 4, iron compound separating device 6, iron compound redissolving device 7, and iron ion removing device 8, the whole of the recovery process for the plating solution 10 was stopped.

With the apparatuses of the respective inventive and comparative examples, tinplate steel strip manufacturing lines, respectively, were operated for twelve months, and the operation rate of the sludge removing devices 2 were investigated. During the period of twelve months, apparatus operation related to iron removal had to be stopped.

As a result, while the operation rate of the sludge removing device 2 in the inventive example was 100%, the operation rate thereof in the comparative example was 50%. Consequently, according to the inventive example, the productivity for tinplate steel strips was improved relative to the case of the comparative example.

EXAMPLE 2

A plating solution used in a plating bath disposed in a tinplate steel strip manufacturing line was supplied to a circulation tank. The plating solution used is a tin methanesulfonate plating solution, and matters such as sludge, iron ion, and tin ion are inevitably mixed into the plating solution. The plating solution was recovered by using the apparatus shown in FIG. 2.

As shown in FIG. 2, the plating solution 10 was supplied from the circulation tank 1 to the sludge removing device 2, and sludge was removed from the plating solution 10. For the sludge removing device 2, a filter press was used. The plating solution 10, from which sludge was removed, was supplied to the solution concentrating device 3. In the solution concentrating device 3, the plating solution 10 was vacuum distillated to vaporizing water, and was then concentrated to a four-times concentration with respect to the concentration of the methanesulfonic acid of the plating solution 10 supplied from the sludge removing device 2. In normal operation, the valve 13 b of the flow path changing device 13 disposed on the discharge side of the solution concentrating device 3 was closed, and the valve 13 a thereof was opened. Thereby, the concentrated plating solution 10 was supplied to the iron compound crystallizing device 4 from the solution concentrating device 3. The concentrated plating solution 10 was cooled in the iron compound crystallizing device 4 to −4° C., whereby the iron methanesulfonate was precipitated. Then, the plating solution 10 and the precipitation were supplied to the iron compound separating device 6 of the iron separating device 5. Therein, the iron methanesulfonate precipitated in the iron compound separating device 6 was separated from the plating solution 10. A centrifugal separator or the like was used as the iron compound separating device 6. The plating solution 10, from which the iron methanesulfonate 11 has been separated in the iron compound separating device 6, was supplied to the circulation tank 1. The iron methanesulfonate 11 was supplied to the iron compound redissolving device 7, and was dissolved therein in industrial water. A redissolved solution 12 obtained thereby was supplied to the iron ion removing device 8, and was adsorbed therein to an ion-exchange resin. The redissolved solution 12, from which the iron ion was removed, was then supplied to the circulation tank 1.

When stopping the operation of at least one of the iron compound crystallizing device 4, iron compound separating device 6, iron compound redissolving device 7, and iron ion removing device 8, the valve 13 b of the flow path changing device 13 was opened, and the valve 13 a thereof was closed. Thereby, the plating solution 10 was supplied to the circulation tank 1 from the solution concentrating device 3. The above is referred to as an inventive example.

Further, as a comparative example, the plating solution used was recovered by using an apparatus shown in FIG. 4. The apparatus operates in substantially the same manner as in the inventive example in the case of the normal operation. However, when stopping the operation of at least one of the iron compound crystallizing device 4, iron compound separating device 6, iron compound redissolving device 7, and iron ion removing device 8, the whole of the recovery process for the plating solution 10 was stopped.

With the apparatuses of the respective inventive and comparative examples, tinplate steel strip manufacturing lines, respectively, were operated for twelve months, and the operation rates of the sludge removing devices 2 and solution concentrating device 3 were investigated. During the period of twelve months, apparatus operation related to iron removal had to be stopped.

As a result, while the respective operation rates of the sludge removing device 2 in the inventive example was 100%, the operation rate thereof in the comparative example was 50%. Further, while the respective operation rate of the solution concentrating device 3 in the inventive example was 95%, the operation rate thereof in the comparative example was 45%. Consequently, according to the inventive example, the productivity for tinplate steel strips was improved relative to the case of the comparative example.

EXAMPLE 3

A plating solution used in a plating bath disposed in a tinplate steel strip manufacturing line was supplied to a circulation tank. The plating solution used is a tin methanesulfonate plating solution, and matters such as sludge, iron ion, and tin ion are inevitably mixed into the plating solution. The plating solution was recovered by using the apparatus shown in FIG. 3.

As shown in FIG. 3, the plating solution 10 was supplied from the circulation tank 1 to the sludge removing device 2, and sludge was removed from the plating solution 10. For the sludge removing device 2, a filter press was used. The plating solution 10, from which sludge was removed, was supplied to the solution concentrating device 3. In the solution concentrating device 3, the plating solution 10 was vacuum distillated to vaporizing water, and was then concentrated to a four-times concentration with respect to the concentration of the methanesulfonic acid of the plating solution 10 supplied from the sludge removing device 2. The plating solution 10 concentrated in the solution concentrating device 3 was supplied to the iron compound crystallizing device 4, and was cooled therein to −4° C., whereby the iron methanesulfonate was precipitated. Then, in normal operation, the valve 13 b of the flow path changing device 13 disposed on the discharge side of the iron compound crystallizing device 4 was closed, and the valve 13 a thereof was opened. Thereby, the plating solution 10 and the precipitation were supplied from the iron compound crystallizing device 4 to the iron compound separating device 6 of the iron separating device 5. The iron methanesulfonate precipitated in the iron compound separating device 6 was separated from the plating solution 10. A centrifugal separator or the like was used as the iron compound separating device 6. The plating solution 10, from which the iron methanesulfonate 11 has been separated in the iron compound separating device 6, was supplied to the circulation tank 1. The iron methanesulfonate 11 was supplied to the iron compound redissolving device 7, and was dissolved therein in industrial water. Then, in the normal operation, the valve 14 b of the redissolved solution flow path changing device 14 disposed on the discharge side of the iron compound redissolving device 7 of the iron separating device 5 was closed, and the valve 14 a thereof was opened. Thereby, a redissolved solution 12 obtained therein was supplied to the iron ion removing device 8. Then, iron ion was adsorbed to the ion-exchange resin in the iron ion removing device 8. The redissolved solution 12, from which the iron ion was removed, was supplied to the circulation tank 1.

When stopping the operation of at least one of the iron compound separating device 6, iron compound redissolving device 7, and iron ion removing device 8, the valve 13 b of the flow path changing device 13 was opened, and the valve 13 a thereof was closed. Thereby, the plating solution 10 was supplied to the circulation tank 1 from the iron compound crystallizing device 4. Especially, when stopping the operation of only the iron ion removing device 8, the valve 13 b of the flow path changing device 13 was closed and the valve 13 a thereof was opened, and concurrently, the valve 14 b of the redissolved solution flow path changing device 14 was opened and valve 14 a thereof was closed. Thereby, the redissolved solution 12 was supplied to the circulation tank 1 from the iron compound redissolving device 7. The above is referred to as an inventive example.

Further, as a comparative example, the plating solution used was recovered by using an apparatus shown in FIG. 4. The apparatus operates in substantially the same manner as in the inventive example in the case of the normal operation. However, when stopping the operation of at least one of the iron compound separating device 6, iron compound redissolving device 7, and iron ion removing device 8, the whole of the recovery process for the plating solution 10 was stopped.

With the apparatuses of the respective inventive and comparative examples, tinplate steel strip manufacturing lines, respectively, were operated for twelve months, and the operation rates of the sludge removing devices 2 and the iron compound crystallizing device 4 were investigated. During the period of twelve months, apparatus operation related to iron removal had to be stopped.

As a result, while the respective operation rates of the sludge removing device 2 in the inventive example was 100%, the operation rate thereof in the comparative example was 50%. Further, while the respective operation rate of the iron compound crystallizing device 4 in the inventive example was 90%, the operation rate thereof in the comparative example was 40%. Consequently, according to the inventive example, the productivity for tinplate steel strips was improved relative to the case of the comparative example.

INDUSTRIAL APPLICABILITY

The apparatus and method according to the present invention is capable of recover a plating solution used for electroplating of steel strips by removing iron and sludge from the plating solution. Further, in the apparatus according to the present invention, even when the operation of a constitutional device(s) related to iron removal is stopped, the continuous electroplating operation can be maintained without reducing the operation rate of the sludge removing device. Consequently, the productivity for electroplated steel strips for steel strips can be improved, and wide industrial contributions can be offered. 

1. A plating solution recovery apparatus for electroplating, comprising: a circulation tank; a sludge removing device; a concentrating device; an iron compound crystallizing device; an iron compound separating device; an iron compound redissolving device; an iron ion removing device; pipelines sequentially connecting the circulation tank, the sludge removing device, the concentrating device, the iron compound crystallizing device, the iron compound separating device, the iron compound redissolving device, and then the iron ion removing device in a downstream direction from a base point coincident with the circulation tank; a pipeline connecting from the iron ion removing device to the circulation tank; a pipeline connecting from the iron compound separating device to the circulation tank; and a flow path changing device connecting to the circulation tank and provided in at least one portion selected from a group of portions, respectively, between the sludge removing device and the concentrating device, between the concentrating device and iron compound crystallizing device, and between the iron compound crystallizing device and the iron compound separating device.
 2. A plating solution recovery apparatus as defined in claim 1, wherein the flow path changing device is provided in the portion between the sludge removing device and the concentrating device.
 3. A plating solution recovery apparatus as defined in claim 1, wherein the flow path changing device is provided in the portion between the concentrating device and the iron compound crystallizing device.
 4. A plating solution recovery apparatus as defined in claim 1, wherein the flow path changing device is provided in the portion between the iron compound crystallizing device and the iron compound separating device.
 5. A plating solution recovery apparatus as defined in claim 1, further comprising a flow path changing device connecting to the circulation tank and provided in a portion between the iron compound redissolving device and the iron ion removing device.
 6. A plating solution recovery apparatus for enabling reuse of a plating solution used to apply electroplating onto a steel strip, the apparatus comprising: a circulation tank for storing the plating solution; a sludge removing device for removing sludge in the plating solution supplied from the circulation tank; a plating solution concentrating device for concentrating the plating solution supplied from the sludge removing device; an iron precipitating device for precipitating an iron compound by cooling the plating solution supplied from the plating solution concentrating device; an iron separating device for separating the iron compound from the plating solution supplied from the iron precipitating device and for redissolving the iron compound in water; an iron removing device for removing an iron ion of a redissolved solution supplied from the iron separating device by means of an ion-exchange resin; and a flow path changing device for supplying the plating solution from the plating solution concentrating device to the circulation tank.
 7. An operating method for the plating solution recovery apparatus as defined in claim 1, wherein, when stopping at least one device from a group consisting of the concentrating device, the iron compound crystallizing device, the iron compound separating device, the iron compound redissolving device, and the iron ion removing device, the flow path for the plating solution is changed to the circulation tank on a side further upstream of a most-upstream side stopped device and in the at least one portion selected from the group of portions, respectively, between the sludge removing device and the concentrating device, between the concentrating device and iron compound crystallizing device, and between the iron compound crystallizing device and the iron compound separating device.
 8. An operating method for the plating solution recovery apparatus as defined in claim 1, wherein, when stopping at least one device from a group consisting of the iron compound crystallizing device, the iron compound separating device, the iron compound redissolving device, and the iron ion removing device, the flow path for the plating solution is changed to the circulation tank on a side further upstream of a most-upstream side stopped device and in the at least one portion selected from the group of portions, respectively, between the sludge removing device and the concentrating device, between the concentrating device and iron compound crystallizing device, and between the iron compound crystallizing device and the iron compound separating device.
 9. An operating method for the plating solution recovery apparatus as defined in claim 1, wherein, when stopping at least one device from a group consisting of the iron compound separating device, the iron compound redissolving device, and the iron ion removing device, the flow path for the plating solution is changed to the circulation tank on a side further upstream of a most-upstream side stopped device and in the at least one portion selected from the group of portions, respectively, between the sludge removing device and the concentrating device, between the concentrating device and iron compound crystallizing device, and between the iron compound crystallizing device and the iron compound separating device.
 10. An operating method for the plating solution recovery apparatus as defined in claim 5, wherein, when stopping the iron ion removing device, the flow path for the redissolved solution is further changed to the circulation tank in a portion between the iron compound redissolving device and the iron ion removing device.
 11. An operating method for the plating solution recovery apparatus, as defined in claim 7, wherein the electroplating solution contains tin methanesulfonate.
 12. A plating solution recovery method for enabling reuse of a plating solution used to apply electroplating onto a steel strip, wherein after the plating solution stored in a circulation tank is supplied to a sludge removing device and sludge in the plating solution is removed; the plating solution is supplied to a plating solution concentrating device, and the plating solution is concentrated therein; the plating solution is supplied to an iron precipitating device, and iron in the plating solution is precipitated therein as an iron compound; the plating solution is supplied to an iron separating device, the iron compound is separated, and the separated iron compound is redissolved in water to be a redissolved solution; the redissolved solution is supplied to an iron removing device, and an iron ion is removed therein by means of an ion-exchange resin; and the plating solution from which the iron compound has been removed in the iron separating device and the redissolved solution from which the iron ion has been removed in the iron removing device are supplied to the circulation tank, wherein, when stopping operation of the iron precipitating device, the iron separating device, or iron removing device, the plating solution is supplied from the plating solution concentrating device to the circulation tank.
 13. A plating solution recovery apparatus as defined in claim 2, further comprising a flow path changing device connecting to the circulation tank and provided in a portion between the iron compound redissolving device and the iron ion removing device.
 14. A plating solution recovery apparatus as defined in claim 3, further comprising a flow path changing device connecting to the circulation tank and provided in a portion between the iron compound redissolving device and the iron ion removing device.
 15. A plating solution recovery apparatus as defined in claim 4, further comprising a flow path changing device connecting to the circulation tank and provided in a portion between the iron compound redissolving device and the iron ion removing device.
 16. An operating method for the plating solution recovery apparatus as defined in claim 13, wherein, when stopping the iron ion removing device, the flow path for the redissolved solution is further changed to the circulation tank in a portion between the iron compound redissolving device and the iron ion removing device.
 17. An operating method for the plating solution recovery apparatus as defined in claim 14, wherein, when stopping the iron ion removing device, the flow path for the redissolved solution is further changed to the circulation tank in a portion between the iron compound redissolving device and the iron ion removing device.
 18. An operating method for the plating solution recovery apparatus as defined in claim 15, wherein, when stopping the iron ion removing device, the flow path for the redissolved solution is further changed to the circulation tank in a portion between the iron compound redissolving device and the iron ion removing device.
 19. An operating method for the plating solution recovery apparatus, as defined in claim 8, wherein the electroplating solution contains tin methanesulfonate.
 20. An operating method for the plating solution recovery apparatus, as defined in claim 9, wherein the electroplating solution contains tin methanesulfonate. 